With the advent of sophisticated equipment in the electrical and electronic fields, it has become necessary that the components of the various pieces of equipment conform to high standards which are set forth in the specifications for these components. For example, circuit boards which are used in relatively complicated pieces of equipment such as main frame computers must be of a relatively high standard of quality in order to function in an efficient manner for a long period of time without deteriorating or breaking down and thus causing an interruption in the function of the machine. This high quality of material is opposed to pieces of equipment requiring a lower standard of quality such as those used in personal computers, television equipment, radios, etc.
Circuit boards upon which a circuit is etched or implanted usually comprise a laminate which is composed of a synthetic polymeric substance and a suitable reinforcement matrix, the composite of which possesses desirable characteristics such as rigidity, low thermal expansion, dimensional stability, low dielectric constant, etc. As will hereinafter be shown, it has now been discovered that a high temperature thermosetting resin composition comprised of one polymer consisting of a three-component polymer and a second polymer comprising a two-component polymer may be cured and used as a circuit board matrix material which will possess the desirable characteristics hereinbefore set forth.
Some previous United States patents have described thermosettable or powder coating compositions. However, these compositions differ from the high temperature thermosetting resin composition of the present invention. For example, U.S. Pat. No. 3,852,236 describes a composition comprising a polyanhydride dissolved in a olefinic monomer such as styrene plus the addition of glycidyl methacrylate or other additives, following which the polymerization of the composition occurs to form a solid infusible resin. In contrast to the teachings found in this patent, the polymeric system of the present invention does not have any volatile olefinic monomers present in the system either during or after curing; the composition of the present invention comprising essentially a polymer blend before curing which, after curing, results in the obtention of a nearly 100% solids system. The system of the present invention incorporates an improved multifunctional terpolymer resin which, upon cross-linking and curing, provides a resin composition which possesses improved properties which are desirable for high speed, high performance circuit boards. As will be hereinafter shown in greater detail in the examples, these properties will include high glass transition temperature, low thermal expansivity and low dielectric constants, these desirable properties not being shown in this patent.
Another U.S. Pat. No. 3,888,943 describes formulations comprising polyanhydrides which are reacted and cured with epoxy-functional polymers. Again, the resin compositions of the present invention which are utilized for printed wiring board applications will exhibit improved properties of the materials of this patent in that the epoxy-functional polymer of the present invention possesses structural groups which will impart the aforementioned desirable properties of high glass transition, low thermal expansion and low dielectric constants. This is in contrast to those which are recited in the patent; for example, the epoxy materials of the patent will possess glass transition temperatures of between 40.degree. and 90.degree. C. While these glass transitions are suitable for powder or powder coatings they are not suitable for use in printed wiring board applications. In contradistinction to these relatively low glass transitions of the patent, the epoxy terpolymer resin compositions of the present invention will possess glass transitions of at least 140.degree. C. In addition, another difference between the patent and the instant application is that the former powder coating composition will have considerable quantities of acrylate and/or methacrylate groups present which would provide undesirable high dielectric constants. Furthermore, the patent also teaches that there is a flow control agent or plasticizer present in the composition. To reiterate and further illustrate the differences between the patent and the present invention, the former discloses the use of a polyanhydride which also contains methacrylate backbone structures, that is groups imparting low glass transitions and high dielectric constants to the finished product, whereas in contrast, the present application requires a high concentration of non-polar rigid groups present in the polyanhydrides to impart the desired characteristics or properties of low dielectric constants and high glass transitions in the final resin composition.
U.S. Pat. No. 2,510,647 discloses a polymeric acenaphthylene or copolymers of acenaphthylene with compounds containing at least one polymerizable ethylene group such as various vinyl compounds as exemplified by methacrylic acid esters or aryl compounds such as styrene. It is noted that each of the references discloses only copolymers rather than the terpolymer composition which will hereinafter be disclosed in greater detail.